The present application relates to a positive electrode active material, a positive electrode using the same and a non-aqueous electrolyte secondary battery. In detail, the present application relates to a positive electrode active material capable of improving a cycle life of a battery, a positive electrode using the same and a non-aqueous electrolyte secondary battery.
In recent years, techniques of portable electronic appliances have conspicuously developed, and electronic appliances such as mobile phones and laptop personal computers have started to be recognized as a fundamental technology for supporting the highly computerized society. Also, research and development regarding high functionalization of these electronic appliances are energetically advanced, and power consumption of these electronic appliances increases steadily in proportion thereto. On the other hand, these electronic appliances are required to be driven for a long period of time, and densification of high energy of a secondary battery which is a drive power source has been inevitably desired. Also, the prolongation of a cycle life has also been desired in view of environmental consideration.
From the viewpoints of occupied volume and mass of a battery to be built in an electronic appliance, it is desired that the energy density of the battery is as high as possible. At present, a lithium ion secondary battery is built in almost all of appliances because it has a high voltage and an excellent energy density as compared with other battery systems.
In general, the lithium ion secondary battery uses a lithium transition metal complex oxide such as lithium cobaltate (LiCoO2) and lithium nickelate (LiNiO2) for a positive electrode and a carbon material for a negative electrode, respectively and is used at an operating voltage in the range of from 4.2 V to 2.5 V. In a unit cell, the fact that a terminal voltage can be increased to 4.2 V largely relies upon excellent electrochemical stability of a non-aqueous electrolyte material, a separator and so on.
For the purposes of realizing higher performances and enlarging applications of such a lithium ion secondary battery, a number of investigations have been advanced. As one of them, for example, it is investigated to increase the energy density of a positive electrode active material starting with lithium cobaltate by a method for increasing a charge voltage or the like, thereby contriving to attain a high capacity of the lithium ion secondary battery.
However, in the case of repeating charge and discharge at a high capacity, there is involved a problem that deterioration of the capacity is caused, whereby the battery life becomes short.
Then, for example, Japanese Patent No. 3172388 discloses a method for enhancing battery characteristics such as a charge and discharge cycle characteristic by coating a metal oxide on the surface of a positive electrode. Also, Japanese Patent No. 3691279 discloses a method for increasing structural stability and thermal stability by coating a metal oxide on the surface of a positive electrode active material.
Also, in coating the surface of a positive electrode active material, effects for improving a cycle characteristic and enhancing thermal stability by a coating form thereof are also investigated. For example, JP-A-7-235292, JP-A-2000-149950, JP-A-2000-156227, JP-A-2000-164214, JP-A-2000-195517 and JP-A-2002-231227 disclose a method for uniformly coating a lithium transition metal complex oxide. Also, JP-A-2001-256979 discloses a positive electrode active material having a lump of a metal oxide deposited on a metal oxide layer.